Functionalized zirconia nanoparticles and high index films made therefrom

ABSTRACT

The present disclosure relates to surface-modified zirconia nanoparticles, methods for making and using the same, and high index of refraction films made therefrom. The provided zirconia nanoparticles are surface modified with ligands that include N-hydroxyurea functionalities. The provided ligands also can contain compatibilizing groups that allow the provided surface-modified zirconia nanoparticles to be incorporated into an organic matrix. High index of refraction films can be made using these organic matrices.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional PatentApplication No. 61/265,968, filed Dec. 2, 2009, the disclosure of whichis incorporated by reference herein in its entirety.

FIELD

The present disclosure relates to surface-modified zirconiananoparticles, methods for making and using the same, and high index ofrefraction films made therefrom.

BACKGROUND

Zirconia nanoparticles have a high refractive index and are useful inorganic matrices to alter optical properties of the matrix. For example,zirconia nanoparticles have been used to increase the index ofrefraction or to increase the x-ray opacity of the organic matrix, whileretaining optical transmission. The extent to which the x-ray opacityand/or refractive index of the organic matrix can be increased isdependent on the percent loading of zirconia in the organic matrix andon characteristics of the zirconia particles such as the percentcrystallinity, the crystalline structure, the primary particle size, andthe degree of association between the primary particles.

Surface modification of zirconia nanoparticl77es can be used to preventor reduce particle agglomeration and to enhance the compatibility of thenanoparticles within an organic matrix. Accordingly, zirconiananoparticles have been treated with a variety of surface modifyingagents such as, for example, carboxylic acids, and/or silanes. Thesetraditional surface modifiers have their drawbacks. For example, organicmatrices containing acrylic acid-derived residues will displace thezirconia-bound carboxylic acid groups with acrylic acid-derived groups.Silane-functionalized zirconia nanoparticles are thermodynamicallyunfavorable and experimentally challenging to prepare.

SUMMARY

There is a need for surface-modifiers that can strongly attach tozirconia nanoparticles and do not suffer from the drawbacks oftraditional surface modifiers. There is also a need for surface-modifiedzirconia nanoparticles that are compatible with a variety of organicmatrices. There is furthermore a need to have composite materials withenhanced optical properties such as high refractive index or x-rayopacity that include surface-modified zirconia nanoparticles dispersedin organic matrices.

In one aspect, surface-modified nanoparticles are provided that includezirconia nanoparticles and at least one non-metallic organic derivative,comprising at least one N-hydroxyurea functionality, wherein at leastsome of the non-metallic organic derivatives are attached to at leastsome of the zirconia nanoparticles.

In another aspect, a method of making surface-modified nanoparticles isprovided that includes combining an aqueous sol ofacetate-functionalized zirconia nanoparticles with at least onenon-metallic organic derivative comprising at least one N-hydroxureafunctionality, or a solution thereof, with a sol to form a mixture andremoving water and displaced acetic acid from the mixture to formsurface-modified nanoparticles.

In yet another aspect, a composition is provided that includes anorganic matrix and surface-modified zirconia nanoparticles attached toat least a portion of the organic matrix, wherein the surface-modifiednanoparticles comprise at least one non-metallic organic derivativecomprising at least one N-hydroxurea functionality.

Finally, in another aspect, a ligand is provided that includes

In this disclosure:

“high refractive index” refers to materials that have a real componentof refractive index above about 1.47;

“N-hydroxyurea functionality” refers to at least one N-hydroxurea groupand can refer to the protonated N-hydroxurea or deprotonatedN-hydroxyurea;

“(meth)acrylic” refers to both derivatives of methacrylic acid and/oracrylic acid;

“non-metallic” refers to compounds that do not contain any metal elementor metalloid elements such as silicon;

“non-metallic organic derivatives containing N-hydroxyureafunctionality” refer to derivatives of N-hydroxyurea that do not containany metals within or attached to the backbone of the derivative but mayinclude the metal salts of the N-hydroxyurea;

“zirconia” refers to a various stoichiometries for zirconium oxides,most typically ZrO₂, and may also be known as zirconium oxide orzirconium dioxide. The zirconia may contain up to 30 weight percent (wt%) of other chemical moieties such as, for example, Y₂O₃ and organicmaterial.

The provided surface-modified zirconia nanoparticles, methods, andcompositions made therefrom can provide high index transparent films.These films can have an index of refraction of greater than about 1.6 oreven higher.

The above summary is not intended to describe each disclosed embodimentof every implementation of the present invention. The brief descriptionof the drawings and the detailed description which follows moreparticularly exemplify illustrative embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing of an embodiment of a providedcomposition.

FIG. 2 is a schematic drawing of another embodiment of a providedcomposition.

DETAILED DESCRIPTION

In the following description, reference is made to the accompanying setof drawings that form a part of the description hereof and in which areshown by way of illustration several specific embodiments. It is to beunderstood that other embodiments are contemplated and may be madewithout departing from the scope or spirit of the present invention. Thefollowing detailed description, therefore, is not to be taken in alimiting sense.

Unless otherwise indicated, all numbers expressing feature sizes,amounts, and physical properties used in the specification and claimsare to be understood as being modified in all instances by the term“about.” Accordingly, unless indicated to the contrary, the numericalparameters set forth in the foregoing specification and attached claimsare approximations that can vary depending upon the desired propertiessought to be obtained by those skilled in the art utilizing theteachings disclosed herein. The use of numerical ranges by endpointsincludes all numbers within that range (e.g. 1 to 5 includes 1, 1.5, 2,2.75, 3, 3.80, 4, and 5) and any range within that range.

Surface-modified nanoparticles are provided that include zirconiananoparticles. Zirconia nanoparticles can be obtained from zirconia solsthat include a plurality of single crystal zirconia particles. In someembodiments, these particles have an average primary particles size ofless than 20 nanometers (nm). These sols can be substantiallynon-associated and can be highly crystalline exhibiting a crystallinityindex of about 0.65 or greater. Of the crystalline phase, about 70% orgreater can exist in combined cubic and tetragonal crystal latticestructures without a crystal phase stabilizer. Exemplary zirconia solscan be obtained via a hydrothermal method. Zirconia sols and methods ofmaking the same are described, for example, in U.S. Pat. Nos. 6,376,590(Kolb et al.), 7,241,437, and 7,429,422 (both Davidson et al.). Thezirconia nanoparticles in sols of these embodiments can contain yttriumin an amount from about 0.1 wt % to 8 wt % based upon the weight ofinorganic oxides in the zirconia particles. The particles can bedispersed in an aqueous medium that includes a carboxylic acid such as,for example, formic acid, acetic acid, propionic acid, butyric acid, ora combination thereof.

The zirconia-containing sols are typically clear. Thezirconia-containing sols often have a high optical transmission due tothe small size and non-associated form of the primary zirconia particlesin the sol. High optical transmission of the sol can be desirable in thepreparation of transparent or translucent composite materials. As usedherein, “optical transmission” refers to the amount of light that passesthrough a sample (e.g., a zirconia-containing sol) divided by the totalamount of light incident upon the sample. The percent opticaltransmission may be calculated using the equation100(I/I_(O))where I is the light intensity passing though the sample and I_(O) isthe light intensity incident on the sample. The optical transmission maybe determined using an ultraviolet/visible spectrophotometer set at awavelength of 600 nm with a 1 cm path length. The optical transmissionis a function of the amount of zirconia in a sol. Forzirconia-containing sols having about 1 wt % zirconia, the opticaltransmission is typically at least 70%, at least 80 percent, or at least90%. For zirconia-containing sols having about 10 wt % zirconia, theoptical transmission is typically at least 20%, at least 50%, or atleast 70%.

The extent of association between the primary particles can bedetermined from the hydrodynamic particle size. The hydrodynamicparticle size can be measured using Photon Correlation Spectroscopy andis described in more detail in PCT Pat. Publ. No. WO 2009/085926 (Kolbet al.). The term “hydrodynamic particle size” and “volume-averageparticle size” are used interchangeably herein. If the particles ofzirconia are associated, the hydrodynamic particle size provides ameasure of the size of the aggregates and/or agglomerates of primaryparticles in the zirconia sol. If the particles of zirconia arenon-associated, the hydrodynamic particle size provides a measure of thesize of the primary particles.

A quantitative measure of the degree of association between the primaryparticles in the zirconia sol is the dispersion index. As used hereinthe “dispersion index” is defined as the hydrodynamic particle sizedivided by the primary particle size. The primary particle size (e.g.,the weighted average crystallite size) can be determined using x-raydiffraction techniques and the hydrodynamic particle size (e.g., thevolume-average particle size) is determined using Photon CorrelationSpectroscopy. As the association between primary particles in the soldecreases, the dispersion index approaches a value of 1 but can besomewhat higher. The zirconia-containing nanoparticles typically have adispersion index of about 1 to 5, about 1 to 4, about 1 to 3, about 1 to2.5, or about 1 to 2.

Photon Correlation Spectroscopy can be used to further characterize thezirconia particles in the sol. For example, the intensity of the lightscattered by particles is proportional to the sixth power of theparticle diameter. Consequently, a light-intensity distribution tends tobe more sensitive to larger particles than smaller ones. One type ofintensity-based size available from Photo Correlation Spectroscopy isthe Z-average Size. It is calculated from the fluctuations in theintensity of scattered light using a cumulants analysis. This analysisalso provides a value called the polydispersity index, which is ameasure of the breadth of the particle size distribution.

The zirconia particles tend to have a Z-average size that is no greaterthan 70 nanometers, no greater than 60 nm, no greater than 50 nm, nogreater than 40 nm, no greater than 35 nm, or no greater than 30 nm. Thepolydispersity index is often less than 0.5, less than 0.4, less than0.3, less than 0.2, or less than 0.1. A polydispersity index near 0.5often indicates a broad particle size distribution while apolydispersity index near 0.1 often indicates a narrow particle sizedistribution.

In addition to the Z-average size and polydispersity index, a completelight-intensity distribution can be obtained during analysis usingPhoton Correlation Spectroscopy. This can further be combined with therefractive indices of the particles and the refractive index of thesuspending medium to calculate a volume distribution for sphericalparticles. The volume distribution gives the percentage of the totalvolume of particles corresponding to particles of a given size range.The volume-average size is the size of a particle that corresponds tothe mean of the volume distribution. Since the volume of a particle isproportional to the third power of the diameter, this distribution isless sensitive to larger particles than an intensity-based size. Thatis, the volume-average size will typically be a smaller value than theZ-average size. The zirconia sols typically have a volume-average sizethat is no greater than 50 nm, no greater than 40 nm, no greater than 30nm, no greater than 25 nm, no greater than 20 nm, or no greater than 15nm. The volume-average size is used in the calculation of the dispersionindex.

The zirconia-containing nanoparticles can optionally contain yttrium.Any yttrium that is present is typically in the form of yttrium oxide.The presence of yttrium in the zirconia-containing nanoparticle usuallyfacilitates the formation of the cubic/tetragonal phases rather than themonoclinic phase. The cubic and tetragonal phases are often preferredbecause they tend to have a higher refractive index and x-ray opacitycompared to the monoclinic phase. These phases also tend to be moresymmetrical, which can be an advantage in some applications when thezirconia-containing nanoparticles are suspended or dispersed in anorganic matrix because they have a minimal effect on the viscosity ofthe organic matrix. Additionally, the percent loading can be higher withthe cubic and tetragonal phases.

The mole ratio of yttrium to zirconium (i.e., moles yttrium÷moleszirconium) in the zirconia-containing nanoparticles is often up to 0.25,up to 0.22, up to 0.20, up to 0.16, up to 0.12, up to 0.08. For example,the mole ratio of yttrium to zirconium can be in the range of from 0 to0.25, from 0 to 0.22, from 0.01 to 0.22, from 0.02 to 0.22, from 0.04 to0.22, from 0.04 to 0.20, from 0.04 to 0.16, or from 0.04 to 0.12.

Expressed differently as oxides, the zirconia-containing nanoparticlesoften contain up to 11 mole percent (mol %) Y₂O₃ based on the moles ofthe inorganic oxides (i.e., Y₂O₃ plus ZrO₂). For example, thezirconia-containing nanoparticles can contain up to 10 mole percent, upto 8 mole percent, up to 6 mol %, or up to 4 mol % Y₂O₃ based on themoles of the inorganic oxides. Some zirconia-containing nanoparticlescontain from 0 to 11 mol %, from 0 to 10 mol %, from 1 to 10 mol %, from1 to 8 mol %, or from 2 to 8 mol % Y₂O₃ based on the moles of theinorganic oxides.

Expressed in yet another manner, the zirconia-containing nanoparticlesoften contain up to 20 weight percent (wt %) Y₂O₃ based on the weight ofthe inorganic oxides (i.e., Y₂O₃ plus ZrO₂). For example, thezirconia-containing nanoparticles can contain up to 18 wt %, up to 16 wt%, up to 12 wt %, up to 10 wt %, or up to 6 wt % Y₂O₃ based on theweight of the inorganic oxides. Some zirconia-containing nanoparticlescontain from 0 to 20 wt %, from 0 to 18 wt %, from 2 to 18 wt %, from 2to 16 wt %, or from 2 to 10 wt % Y₂O₃ based on the weight of theinorganic oxides.

The zirconia-containing nanoparticles often contain at least someorganic material in addition to inorganic oxides. The organic materialcan be attached to the surface of the zirconia particles and oftenoriginates from the carboxylate species (anion, acid, or both) includedin the feedstock or formed as a byproduct of the hydrolysis andcondensation reactions. That is, the organic material is often adsorbedto the surface of the zirconia-containing nanoparticles. The zirconiaparticles often contain up to 15 wt %, up to 12 wt %, up to 10 wt %, upto 8 wt %, or up to 6 wt % organic material based on the weight of theparticles.

The zirconia-containing nanoparticles often contain less than 3milligrams of an alkali metal such as sodium, potassium, or lithium pergram of zirconium in the nanoparticles. For example, the amount ofalkali metal can be less than 2 milligrams (mg) per gram of zirconium,less than 1 mg per gram of zirconium, less than 0.6 mg per gram ofzirconium, less than 0.5 mg per gram of zirconium, less than 0.3 mg pergram of mg, less than 0.2 mg per gram of zirconium, or less than 0.1 mgper gram of zirconium.

Likewise, the zirconia-containing nanoparticles often contain less than3 mg of an alkaline earth such as calcium, magnesium, barium, orstrontium per gram of zirconium in the nanoparticles. For example, theamount of alkaline earth can be less than 2 mg per gram of zirconium,less than 1 mg per gram of zirconium, less than 0.6 mg per gram ofzirconium, less than 0.5 mg per gram of zirconium, less than 0.3 mg pergram of zirconium, less than 0.2 mg per gram of zirconium, or less than0.1 mg per gram of zirconium.

The zirconia-containing nanoparticles can be substantially crystalline.Crystalline zirconia tends to have a higher refractive index and higherx-ray scattering capability than amorphous zirconia. Due to thedifficulty in separately quantifying cubic and tetragonal crystalstructures for small particles using x-ray diffraction (i.e., the (111)peak for cubic zirconia often overlaps with the (101) peak fortetragonal zirconia). If yttrium is present, at least 70% of the totalpeak area of the x-ray diffraction scan is attributed to a cubicstructure, tetragonal structure, or a combination thereof with thebalance being monoclinic. For example, at least 75%, at least 80%, or atleast 85% of the total peak area of some x-ray diffraction scans can beattributed to a cubic crystal structure, tetragonal crystal structure,or a combination thereof. Cubic and tetragonal crystal structures tendto promote the formation of low aspect ratio primary particles having acube-like shape when viewed under an electron microscope.

The zirconia particles usually have an average primary particle size nogreater than 50 nm, no greater than 40 nm, no greater than 30 nm, nogreater than 25 nm, no greater than 20 nm, no greater than 15 nm, or nogreater than 10 nm. The primary particle size, which refers to thenon-associated particle size of the zirconia particles, can bedetermined by x-ray diffraction.

Nanoparticles, such as zirconia nanoparticles, typically agglomerate andit can be difficult to achieve good dispersions of them in media, suchas aqueous or organic media. In particular, it can be difficult to getdispersed nanoparticles within a polymer matrix due to the tendency ofthe nanoparticles to associate into agglomerates. Therefore, it can beadvantageous to modify the surface of the nanoparticles so thatagglomeration becomes thermodynamically unfavorable. Surfacemodification involves reacting the zirconia particles with a surfacemodification agent or combination of surface modification agents thatattach to the surface of the zirconia nanoparticles and that modify thesurface characteristics of the zirconia particles.

Surface modification agents can be represented by the formula A-B wherethe A group is capable of attaching to the surface of a zirconiaparticle, and where B is a compatibilizing group. The A group can beattached to the surface by absorption, formation of an ionic bond,formation of a covalent bond, or a combination thereof. Suitableexamples of A groups include, for example, N-hydroxyureas. Thecompatibilizing groups B can be reactive or nonreactive and can be polaror nonpolar moieties. Polar compatibilizing groups can include ahydroxyl group, a carboxylic acid group, an amine group, a thiol group,an epoxide group, an aziridine group, an azide group, a halide group, analkyne group, an olefin group, an acrylate group, a methacrylate group,and combinations thereof.

Nonpolar compatibilizing groups can include an alkyl group, an alkylenegroup, a heteroalkyl group, an aryl group, an arylene group, andcombinations thereof. Of particular importance are surface-modificationagents that have compatibilization groups (B) that are compatible withpolymeric systems. For example, surface modification agents that have(meth)acrylate compatibilizing groups can be useful to disperse zirconiananoparticles in (meth)acrylic polymer systems. These agents can beobtained, for example, by reacting hydroxylamine with anisocyanate-functionalized (meth)acrylate compound to obtain(meth)acrylate-functionalized N-hydroxyureas that can bind to zirconiananoparticles.

N-hydroxyureas are structurally and chemically similar to hydroxamicacids which are a well-studied class of compounds. Hydroxamic acids areknown to form self-assembled monolayers on native oxides of metals asdescribed by J. P. Folkers, et al., “Self-Assembled Monolayers ofLong-Chain Hydroxamic Acids on Native Oxides of Metals,” Langmuir, 11,813 (1998). Both N-hydroxyureas and hydroxamic acids have been used inmedicinal chemistry applications. For example, N-hyroxyureas can inhibitmany enzymes including proteases, ureases, oxygenases, hydrolases, andperoxidases and can provide antibacterial, antifungal, and insecticidalprotection for plants. Synthetically, N-hydroxyureas can be obtained byreaction between a hydroxylamine and a carbonyl-based electrophile, suchas an isocyanate or carbamyl chloride. N-hydroxyureas can be made byreacting isocyanates or carbamyl chlorides with hydroxylamines asdisclosed, for example, in GB 921,536 (Steinbrunn). Alternatively,coupling reactions between a hydroxylamine and a carbamic acid can becarried out directly using coupling and/or activating agents that areuseful in the synthesis of amides. These agents include, for example,carbodiimides.

The provided surface-modified nanoparticles include at least onenon-metallic organic derivative that comprises at least oneN-hydroxyurea as discussed above. In some embodiments, thesurface-modified nanoparticles include at least one non-metallic organicderivative that has the formula:

In this formula R₁ can be hydrogen, an alkyl group, a cycloalkyl group,an aryl group, a heteroaryl group, an alkylaryl group, analkylheteroaryl group and a heterocycloalkyl group. R₂ and R₃,independently, can include a moiety selected from alkyl, alkylene,heteroalkyl, aryl, arylene, and combinations thereof. Typically alkylgroups have from about 1 to about 20 carbon atoms and can be branched orunbranched. Cycloalkyl groups typically include 5-12 membered rings suchas, for example, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, orcyclododecyl groups. Aryl groups include phenyl, naphthyl, anthracenyl,phenanthenyl, biphenyl, or any other aryl ring systems. R² can be alkyl,alkylene, heteroalkyl, aryl, arylene, or combinations thereof.Additionally R² can further include at least one of a hydroxyl, amino,thioether, thiol, carboxy, carbonyl, alkylether, alkynyl, alkenyl,halogen, (meth)acrylate or combination thereof. R² can also includeadditional N-hydroxyurea groups.

To make the provided surface-modified zirconia nanoparticles, an aqueoussol of acetate-functionalized zirconia nanoparticles is provided asdescribed above. A solution is mixed with the sol that includes at leastone non-metallic organic derivative that includes at least oneN-hydroxyurea functionality. The mixture is then, optionally, heated andwater and displaced acetic acid is removed from the mixture to formsurface-modified zirconia nanoparticles that can be isolated as a powderor slurry. Alternatively, the provided surface-modified zirconiananoparticles can be made in one pot from 2-isocyanatoethylmethacrylate, hydroxylamine, and acetate-stabilized zirconiananoparticles as described more fully in the Example section below.

In another aspect, a composition is provided that includes an organicmatrix and surface-modified zirconia nanoparticles attached to at leasta portion of the organic matrix. The surface-modified zirconiananoparticles include at least one non-metallic organic derivative thatincludes at least one N-hyroxyurea functionality. The organic matrix canbe any polymer or copolymer matrix. The polymer or copolymer matrix canbe derived from monomers, oligomers, copolymers, or a combinationthereof. Exemplary polymers include poly(meth)acrylates, polyesters,polyurethanes, polystryenes, epoxies, vinyl polymers, (methacrylated)polyesters, and combinations thereof. The surface-modified zirconiananoparticle sols can also be combined with other types of polymers, forexample, polyolefins, polycarbonates, and polyimides.

In some embodiments, surface-modified zirconia nanoparticles can bedispersed and bonded into optically clear organic matrices to producehigh refractive index composites. For example, zirconia nanoparticlesthat have been surface modified with carboxylates or silanes can beincorporated into organic matrices that contain ultraviolet curablemonomers to form materials with refractive indices greater than 1.47. Itis contemplated that the provided N-hydroxyurea-functionalized zirconiananoparticles will be compatible in these systems as well.

Surface-modified zirconia nanoparticles can be produced with smallorganic ligands attached to the nanoparticles. Typically, all organicfilms can be produced that have refractive indices as high as about1.45-1.65 by incorporating aromatic groups, halogens or other groupsthat have high density and dielectric constant. But it is very hard tomake an optically clear polymeric film that has a refractive index muchhigher than 1.65. Zirconia nanoparticles that have been surface-modifiedby low molecular weight N-hydroxyureas such as, for example, those madefrom 2-isocyanatoethyl methacrylate and hydroxylamine, can beincorporated into acrylic films which, after curing, can produce clearfilms having a refractive index of greater than 1.65, even greater than1.70. These high index films can be useful to make optical displayelements or other optical elements that have low reflection (forexample, anti-reflective properties).

FIG. 1 is a schematic of an embodiment of an article that includesprovided surface-modified zirconia nanoparticles incorporated into anorganic matrix. Article 100 includes optically transmissive substrate101 that includes primer 103 disposed thereupon. High index ofrefraction hardcoat 105 is adjacent to and in contact with primer 103.FIG. 2 is a schematic drawing of an embodiment of an article thatincludes an antireflection film. Article 200 includes substrate 201,primer 203, and high index hardcoat 205 as illustrated in FIG. 1. Atopand in contact with hardcoat 205 is low index optical coating 207. Lowindex optical coating 207 is a quarter wavelength coating that has anindex of refraction of 1.43

In some embodiments, the organic matrix can be an adhesive composition.Typically the adhesive compositions can be (meth)acrylicpressure-sensitive adhesives. The adhesive compositions can be derivedfrom precursors that include from about 75 to about 99 parts by weightof an alkyl acrylate having 1 to 14 carbons in the alkyl group. Thealkyl acrylate can include aliphatic, cycloaliphatic, or aromatic alkylgroups. Useful alkyl acrylates (i.e., acrylic acid alkyl ester monomers)include linear or branched monofunctional acrylates or methacrylates ofnon-tertiary alkyl alcohols, the alkyl groups of which have from 1 up to14 and, in particular, from 1 up to 12 carbon atoms. Useful monomersinclude, for example, 2-ethylhexyl (meth)acrylate, ethyl (meth)acrylate,methyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl(meth)acrylate, pentyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl(meth)acrylate, 2-octyl acrylate, isononyl (meth)acrylate, n-butyl(meth)acrylate, isobutyl (meth)acrylate, hexyl (meth)acrylate, n-nonyl(meth)acrylate, isoamyl (meth)acrylate, n-decyl (meth)acrylate, isodecyl(meth)acrylate, dodecyl (meth)acrylate, isobornyl (meth)acrylate,cyclohexyl (meth)acrylate, phenyl meth(acrylate), benzyl meth(acrylate),and 2-methylbutyl (meth)acrylate, biphenyloxyethyl acrylate (BPEA),6-(2-biphenoxy)hexyl acrylate and combinations thereof.

The provided adhesive composition precursors can also include from about1 to about 25 parts of a copolymerizable polar monomer such as(meth)acrylic monomer containing carboxylic acid, amide, urethane, orurea functional groups. Useful carboxylic acids include acrylic acid andmethacrylic acid. Weak polar monomers like N-vinyl lactams may also beincluded. A useful N-vinyl lactam is N-vinyl caprolactam. In general,the polar monomer content in the adhesive can include less than about 10parts by weight or even less than about 5 parts by weight of one or morepolar monomers. Useful amides include N-vinyl caprolactam, N-vinylpyrrolidone, (meth)acrylamide, N-methyl (meth)acrylamide, N,N-dimethylacrylamide, N,N-dimethyl meth(acrylamide), and N-octyl (meth)acrylamide.

The pressure sensitive adhesive can be inherently tacky. If desired,tackifiers can be added to the precursor mixture before formation of thepressure sensitive adhesive. Useful tackifiers include, for example,rosin ester resins, aromatic hydrocarbon resins, aliphatic hydrocarbonresins, and terpene resins. In general, light-colored tackifiersselected from hydrogenated rosin esters, terpenes, or aromatichydrocarbon resins can be used.

Other materials can be added for special purposes, including, forexample, oils, plasticizers, antioxidants, UV stabilizers, pigments,curing agents, polymer additives, and other additives provided that theydo not significantly reduce the optical clarity of the pressuresensitive adhesive.

The provided adhesive compositions (that include surface-modifiedzirconia nanoparticles) may have additional components added to theprecursor mixture. For example, the mixture may include amultifunctional crosslinker. Such crosslinkers include thermalcrosslinkers which are activated during the drying step of preparingsolvent coated adhesives and crosslinkers that copolymerize during thepolymerization step. Such thermal crosslinkers may includemultifunctional isocyanates, aziridines, multifunctional(meth)acrylates, and epoxy compounds. Exemplary crosslinkers includedifunctional acrylates such as 1,6-hexanediol diacrylate ormultifunctional acrylates such as are known to those of skill in theart. Useful isocyanate crosslinkers include, for example, an aromaticdiisocyanate available as DESMODUR L-75 from Bayer, Cologne, Germany.Ultraviolet, or “UV”, activated crosslinkers can also be used tocrosslink the pressure sensitive adhesive. Such UV crosslinkers mayinclude benzophenones and 4-acryloxybenzophenones.

In addition, the precursor mixtures for the provided adhesivecompositions can include a thermal or a photoinitiator. Examples ofthermal initiators include peroxides such as benzoyl peroxide and itsderivatives or azo compounds such as VAZO 67, available from E.I. duPont de Nemours and Co. Wilmington, Del., which is2,2′-azobis-(2-methylbutyronitrile), or V-601, available from WakoSpecialty Chemicals, Richmond, Va., which isdimethyl-2,2′-azobisisobutyrate. A variety of peroxide or azo compoundsare available that can be used to initiate thermal polymerization at awide variety of temperatures. The precursor mixtures can include aphotoinitiator. Particularly useful are initiators such as IRGACURE 651,available from Ciba Chemicals, Tarrytown, N.Y., which is2,2-dimethoxy-2-phenylacetophenone. Typically, the crosslinker, ifpresent, is added to the precursor mixtures in an amount of from about0.05 parts by weight to about 5.00 parts by weight based upon the otherconstituents in the mixture. The initiators are typically added to theprecursor mixtures in the amount of from 0.05 parts by weight to about 2parts by weight. The precursor mixtures can be polymerized and/orcross-linked using actinic radiation or heat to form the adhesivecomposition as described above and in the Examples below.

The pressure-sensitive adhesive precursors can be blended with theprovided surface-modified zirconia nanoparticles to form an opticallytransparent or translucent mixture. Typically, the mixtures can containup to about 25 wt % zirconia or even more. The mixture can bepolymerized by exposure to heat or actinic radiation (to decomposeinitiators in the mixture). This can be done prior to the addition of across-linker to form a coatable syrup to which, subsequently, one ormore crosslinkers, and additional initiators can be added, the syrup canbe coated on a liner, and cured (i.e., cross-linked) by an additionalexposure to initiating conditions for the added initiators.Alternatively, the crosslinker and initiators can be added to themonomer mixture and the monomer mixture can be both polymerized andcured in one step. The desired coating viscosity can determine whichprocedure used. The disclosed adhesive compositions or precursors may becoated by any variety of known coating techniques such as roll coating,spray coating, knife coating, die coating, and the like. Alternatively,the adhesive precursor composition may also be delivered as a liquid tofill the gap between the two substrates and subsequently be exposed toheat or UV to polymerize and cure the composition. The thickness of theadhesive layer in the articles of disclosure tends to be greater thanabout 5 micrometers (μm), greater than about 10 μm, greater than about15 μm, or even greater than about 20 μm. The thickness is often lessthan about 1000 μm, less than about 250 μm, less than about 200 μm, oreven less than about 175 μm. For example, the thickness can be fromabout 5 to about 1000 μm, from about 10 to about 500 μm, from about 25to about 250 μm, or from about 50 to about 175 μm.

In some embodiments, compositions that include surface-modified zirconiananoparticles can be radioopaque. By radioopaque it is meant that thecompositions absorb or scatter X-ray radiation. These materials can beuseful, for example, in dental or medical applications.

Objects and advantages of this invention are further illustrated by thefollowing examples, but the particular materials and amounts thereofrecited in these examples, as well as other conditions and details,should not be construed to unduly limit this invention.

EXAMPLES

Zirconia nanoparticles were functionalized withmethacrylate-functionalized N-hydroxyureas. The functionalized particleswere then combined with multifunctional acrylates and a photoinitiatorbefore being cured under UV irradiation. Nanozirconia-filled hardcoatswere prepared with refractive indices ranging from 1.699-1.743. Thefilms were clear and colorless.

Preparation of Nanozirconia-Filled High Refractive Index Hardcoats

All polymer anti-reflection films (APAR) were prepared on both cellulosetriacetate (TAC) and polyethyleneterephthalate (PET) substrates. Thefilms were clear and colorless. Furthermore, the optical performance ofthe TAC film was comparable to a control film made using nanozirconiafunctionalized with 3-(trimethoxysilyl)propyl methacrylate (Table 1).The transmission (95.3%), haze (0.30%) and reflectivity (1.7%) of theexperimental film were excellent.

TABLE 1 Optical Characteristics of APAR Films^(a) % T % Haze %Reflectivity Experimental 95.3 0.30 1.7 APAR^(b) Control APAR^(c) 95.20.23 1.7 ^(a)APAR films were prepared on TAC film. ^(b)The ExperimentalAPAR was prepared using nanozirconia modified with N-hydroxyurea 1.^(c)The Control APAR was prepared using nanozirconia modified with3-(trimethoxysilyl)propyl methacrylate.I. N-Hydroxyurea Synthesis

N-hydroxyureas were synthesized by the straightforward reaction betweenhydroxyl amine and an isocyanate (Scheme (1)). Two representativeligands were synthesized.

General Procedures.

All reactions were performed in round-bottomed flasks using commercialreagents as received. The flasks were gently sealed with a plastic cap,and the reactions were run under an ambient atmosphere with magneticstirring.

Materials

Commercial reagents were used as received. SR 399 (dipentaerythritolpentaacrylate) and SR 601 (ethoxylated (4) bisphenol A diacrylate) wereobtained from Sartomer. CN4000 is a fluorinated acrylate oligomer with arefractive index of 1.341 and is available from Sartomer. IRGACURE® 2959(1-[4-(2-Hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propane-1-one),IRGACURE® 127(2-Hydroxy-1-{4-[4-(2-hydroxy-2-methyl-propionyl)-benzyl]-phenyl}-2-methyl-propan-1-one),and IRGACURE 184 (1-Hydroxy-cyclohexyl-phenyl-ketone) are available fromCIBA Specialty Chemicals. Unstabilized tetrahydrofuran was obtained fromEMD Chemicals Inc. 1-Methoxy-2-propanol was purchased from J. T. Baker.Hydroxylamine (as a 50 wt % aqueous solution) was obtained from AlfaAesar. 2-Isocyanatoethyl methacrylate is available from Sigma-Aldrich.Isophorone diisocyanate was obtained from TCI America.

The ZrO₂ aqueous sol used in the below examples was prepared accordingto the procedure outlined in Example 6 of U.S. Pat. No. 7,429,422(Davidson et al.). HOSTAPHAN 3SAB is a polyester film available fromMitsubishi Polyester Film, Inc. SILPHAN S36 M74A is a silicone-coatedpolyester (PET) release liner available from Siliconature. Cellulosetriacetate film (TAC film) was obtained from Fujufilm, Tokyo, Japan.

Instrumentation

Proton nuclear magnetic resonance (¹H NMR) spectra and carbon nuclearmagnetic resonance (¹³C NMR) spectra were recorded on a 400 or 500 MHzspectrometer. Chemical shifts for protons are reported in parts permillion downfield from tetramethylsilane and are referenced to residualprotium in the NMR solvent (CHCl₃: δ 7.26; (CD₂H)₂SO: δ 2.50; CD₂HOH: δ3.51). Chemical shifts for carbon are reported in parts per milliondownfield from tetramethylsilane and are referenced to the carbonresonances of the solvent (CDCl₃: δ 77.16; (CD₃)₂SO: δ 39.52; CD₃OD: δ49.00). Data are presented as follows: chemical shift, integration,multiplicity (br=broad, s=singlet, d=doublet, t=triplet, q=quartet,quint.=quintuplet, m=multiplet), coupling constants in Hertz (Hz), andassignment. Refractive indices of cured films were measured on aMetricon 2010 Prism Coupler.

Preparatory Example of Ligand 1

A 250 mL round-bottomed flask equipped with a magnetic stir bar wascharged with a 50 wt % solution of hydroxylamine in water (5.0 mL, 2.80g, 84.8 mmol). Tetrahydrofuran (85 mL) was added with stirring and themixture became homogeneous. 2-Isocyanatoethyl methacrylate (12.0 mL,13.2 g, 84.8 mmol) was added to the reaction mixture over a period of 2minutes. The reaction vessel was gently capped with a yellow plasticcap. After 18 hours, the clear, colorless, and homogeneous reactionmixture was concentrated approximately to dryness in vacuo to a clear,colorless, viscous liquid. Upon standing, the liquid slowly solidifiedto provide Ligand 1 (18.9 g, 100 mmol, 118%) as a white solid. Theexcess mass was due to residual tetrahydrofuran solvent. ¹H NMR (400MHz, DMSO) δ 8.60 (1H, s, NHOH), 8.38 (1H, s, NHOH), 6.88 (1H, t, J=5.8Hz, NHCH₂), 6.05 (1H, s, CH₂C═C), 5.67 (1H, s, CH₂C═C), 4.09 (2H, t,J=5.7 Hz, CH₂OC═O), 3.36-3.28 (2H, m, CH₂NHC═O), 1.87 (3H, s, CH₃); ¹³CNMR (101 MHz, DMSO) δ 166.6, 161.6, 135.9, 125.9, 63.7, 18.1; MS (ES)m/z for C₇H₁₁N₂O₄ [M-H]⁻ calcd. 187.1, found 187.0.

Preparatory Example of Ligand 2

A 50 mL round-bottomed flask equipped with a magnetic stir bar wascharged with isophorone diisocyanate (5.0 mL, 5.25 g, 23.6 mmol).2-Hydroxyethyl methacrylate (2.86 mL, 3.07 g, 23.6 mmol) was addedslowly with stirring over a period of 2 minutes. The reaction was sealedwith a rubber septum, placed in an oil bath, and heated to 50° C. withstirring. A 20 gauge needle was added to the rubber septum to vent thereaction to air. After 66 hours, the reaction mixture was cooled to roomtemperature to provide the product as a clear, colorless, viscousliquid. The reaction product was then used directly in the nextreaction.

A 100 mL round-bottomed flask equipped with a magnetic stir bar wascharged with tetrahydrofuran (25 mL) and a 50 wt % solution ofhydroxylamine in water (1.40 mL, 0.784 g, 23.74 mmol). The crude productfrom the previous reaction was then slowly added to the stirred reactionvia pipette over a period of 5 minutes. Tetrahydrofuran (4×2.5 mL) wasused to rinse the flask containing the product from the previousreaction and the rinses were added to the reaction. The reaction wascapped with a plastic cap equipped with a 16 gauge needle to vent toair. After 24 hours, the reaction mixture was concentrated in vacuo to afoamy white solid. The product was further dried under high vacuum toprovide the desired product 2 as a mixture of isomers (7.99 g, 20.7mmol, 87.9%) as a white solid. ¹H NMR (400 MHz, DMSO) analysis of theproduct was consistent with the desired product as a mixture of isomers.

Example 1 One-Pot Preparation of Methacrylate-Functionalized ZirconiaNanoparticles with Ligand 1

A 1 L round-bottomed flask equipped with a magnetic stir bar was chargedwith tetrahydrofuran (250 mL) and a 50 wt % solution of hydroxylamine inwater (15.0 mL, 8.40 g, 254 mmol). The reaction was cooled to 0° C. inan ice bath. With stirring, 2-isocyanatoethyl methacrylate (36.0 mL,39.5 g, 255 mmol) was added slowly to the reaction mixture over a periodof 20 minutes. After 2 hours, the ice bath was removed and the reactionwas allowed to warm to room temperature. After an additional 1 hour, thereaction was sampled. ¹H NMR (500 MHz, DMSO) analysis was consistentwith clean formation of the desired N-hydroxyurea product, and alsoshowed that the starting material (2-isocyanatoethyl methacrylate) hadbeen consumed. An aqueous solution of acetate-stabilized zirconia(442.62 g sol, 181.66 g ZrO₂) was added to the reaction. The reactionmixture was stirred for 20 minutes. Then, 1-methoxy-2-propanol (100 mL)was added. The reaction mixture was concentrated in vacuo toapproximately 450 g. Then, the solution was diluted with1-methoxy-2-propanol to approximately 900 g and concentrated in vacuo toabout 430-500 g four times. After the final in vacuo concentration, themixture was diluted with 1-methoxy-2-propanol to 508 g. The finalsolution was 42 wt % solids, 33 wt % ZrO₂, and 79 wt % of the solidswere ZrO₂. Based on the percent solids and final mass of solution, theoverall yield was 93%. The solution of functionalized zirconiananoparticles was milky white but well dispersed and stable.

Example 2 Hardcoat Prepared Using Ligand 1

An aqueous solution of acetate-stabilized zirconia (4.00 g sol, 1.65 gZrO₂) was added to a 20 mL glass vial. Ligand 1 (0.434 g, 2.31 mmol) wasadded and the solution was mixed well. The mixture was sonicated for 45minutes to provide a solution with a small insoluble flake of ligandremaining 1-methoxy-2-propanol (8.0 mL) was added. The solution wasmixed well and sonicated again for 30 minutes to provide a cloudysolution. The mixture was concentrated in vacuo to approximately 4.0 mLas a thick solution. 1-methoxy-2-propanol (8.0 mL) was added, and thesolution was mixed well and sonicated again for 25 minutes to provide acloudy solution. The mixture was concentrated in vacuo to approximately3-4 mL. SR 399 (0.265 g, 0.505 mmol) and IRGACURE 2959 (0.0360 g, 0.161mmol) were added. The mixture was sonicated for 10 minutes to provide aslightly cloudy solution. The mass of the solution was 3.9976 g (60 wt %solids, 69 wt % of the solids were ZrO₂). A handspread was pulled onto aPET liner (2 mil 3SAB, available from Mitsubishi Polyester Film, Inc.)using a 2 mil gap to provide a clear and colorless wet film. The filmwas dried at 70° C. for 25 minutes and then cooled to room temperature.A release liner (SILPHAN S36 M74 A 152 mm from Siliconature, Treviso,Italy) was placed on the top of the coating. The film was placed under alamp (λ=350 nm) and irradiated for approximately 23 hours. The finalcured film was clear, colorless, and transparent. The film was 15±2 μmthick. The refractive index of the film was 1.699.

Example 3 High Index Film

Using the procedure of Example 2, a film was prepared fromacetate-stabilized zirconia (4.00 g sol, 1.65 g ZrO₂), ligand 1 (0.434g, 2.31 mmol) SR 399 (0.151 g, 0.288 mmol), and IRGACURE 2959 (0.0360 g,0.161 mmol). The mass of the final solution was 4.0018 g (57 wt %solids, 73 wt % of the solids were ZrO₂). The final cured film wasclear, colorless, and transparent. The film was 8.7±1.0 μm thick. Therefractive index of the film was 1.721.

Example 4 High Index Film

Using the procedure of Example 2, a film was prepared fromacetate-stabilized zirconia (4.00 g sol, 1.65 g ZrO₂), ligand 1 (0.434g, 2.31 mmol) SR 399 (0.0797 g, 0.152 mmol), and IRGACURE 2959 (0.0360g, 0.161 mmol). The mass of the final solution was 4.0092 g (55 wt %solids, 75 wt % of the solids were ZrO₂). The final cured film wasclear, colorless, and transparent. The film was 7.1±0.8 μm thick. Therefractive index of the film was 1.743.

Example 5 Hardcoat Prepared from Ligand 2

An aqueous solution of acetate-stabilized zirconia (2.00 g sol, 0.821 gZrO₂) was added to a 20 mL glass vial. Ligand 2 (0.395 g, 1.03 mmol) wasadded and the solution was mixed well. The mixture was sonicated for 15minutes to provide a homogeneous solution. 1-methoxy-2-propanol (8.0 mL)was added. The solution was mixed well and sonicated again for 15minutes to provide a well-dispersed solution. The mixture wasconcentrated in vacuo to approximately 1.5-2.0 mL as a thick solution.SR 399 (0.105 g, 0.200 mmol), IRGACURE 2959 (0.018 g, 0.080 mmol), and1-methoxy-2-propanol (0.25 mL) were added. The mass of the solution was2.199 g (61 wt % solids, 39 wt % solvent, 61 wt % of the solids wereZrO₂). The mixture was sonicated for 15 min to provide a slightly cloudysolution. A handspread was pulled onto a 2 mil (μm) PET liner (50 3SAB,available from Mitsubishi Polyester Film, Inc., Greer, S.C.) using a 1mil (25 μm) gap to provide a clear and colorless wet film. The film wasdried at 80° C. for 9 minutes and then cooled to room temperature. Arelease liner (SILPHAN S36 M74 A 152 mm) was placed on the top of thecoating. The edges were taped down to seal out air. The film was placedunder a lamp (λ=350 nm) and irradiated for approximately 21 hours. Thefinal cured film was clear, colorless, and transparent.

Example 6 Polymeric Anti-Reflection Film

A polymeric anti-reflection film was made using N-hydroxyurea-modifiedzirconia. A stock solution of nanozirconia functionalized with ligand 1was prepared. An aqueous sol of acetate-stabilized nanozirconia (50.00 gsol, 20.61 g ZrO₂) was added to a 250 mL round-bottomed flask. Ligand 1(5.431 g, 28.86 mmol) was added and the solution was mixed well. Themixture was sonicated for 75 minutes to provide a well-dispersedhomogeneous solution. 1-methoxy-2-propanol (100 mL) was added. Thesolution was mixed well and sonicated again for 45 minutes to provide aslightly cloudy solution. The mixture was concentrated in vacuo toapproximately 50-60 mL as a thick solution. 1-methoxy-2-propanol (100mL) was added, and the solution was mixed well and sonicated again for45 minutes to provide a slightly cloudy solution. The mixture wasconcentrated in vacuo to approximately 50-60 mL. 1-methoxy-2-propanol(100 mL) was added, and the solution was mixed well and sonicated againfor 50 minutes to provide a slightly cloudy solution. The mixture wasconcentrated in vacuo to approximately 50-55 mL. The mass of thesolution was 52.5516 g (50 wt % solids, 79 wt % of the solids wereZrO₂). The solution of functionalized zirconia nanoparticles was cloudywhite but was homogeneously dispersed.

The high index coating formulation was prepared by blending theN-hydroxyurea-functionalized zirconia nanoparticles with acrylatemonomers and photoinitiator. Briefly, 15 g ofN-hydroxyurea-functionalized nanozirconia (50 wt % solid in1-methoxy-2-propanol), 0.844 g of SR601 (Sartomer, Exton, Pa.), 0.844 gof SR399 (Sartomer, Exton, Pa.), 0.02 g of IRGACURE 184 (Ciba, HighPoints, N.C.), and 3.7 g of methyl acetyl ketone, were mixed togetherwith stirring to form a homogenous solution.

The high index coating solution was then applied on top of “MELINEX 618”primed PET films or TAC films using a #9 wire-wound rod (obtained fromRD Specialties, Webster, N.Y.), respectively. The resulting films werethen dried in an oven at 85° C. for 1 min, then cured using a FusionUV-Systems Inc. Light-Hammer 6 UV (Gaithersburg, Md.) processor equippedwith an H-bulb, operating under nitrogen atmosphere at 75% lamp power ata line speed of 30 feet/min (1 passes). The refractive index of theresulting film was measured as 1.70.

The low index coating formulation was prepared according to U.S. Pat.No. 7,615,293. The low index coating solution (3 wt % solid) wasover-coated on the high index coating (prepared as above), using #4 rodand air dried for 2 min. Then resulting films were then cured using aFusion UV-Systems Inc. Light-Hammer 6 UV (Gaithersburg, Md.) processorequipped with an H-bulb, operating under nitrogen atmosphere at 100%lamp power at a line speed of 10 feet/min (1 passes).

The antireflection films on both TAC and PET were clear and colorless.The optical properties of the film on the TAC liner were measured. Thetransmission was 95.3%, the haze was 0.3%, and the reflectivity was1.7%. The film passed color stability testing after 288 hours at 83° C.under 0.5 W/cm² irradiation.

What is claimed is:
 1. Surface-modified nanoparticles comprising:zirconia nanoparticles; and at least one non-metallic organicderivative, comprising at least one N-hydroxyurea functionality, whereinat least some of the non-metallic organic derivatives are attached to atleast some of the zirconia nanoparticles.
 2. Surface-modifiednanoparticles according to claim 1, wherein the at least onenon-metallic organic derivative further comprises a compatibilizinggroup.
 3. Surface-modified nanoparticles according to claim 2, whereinthe compatibilizing group is polar, nonpoplar, or a combination thereof.4. Surface-modified nanoparticles according to claim 3, wherein thepolar compatibilizing group, if present, is selected from a hydroxylgroup, a carboxylic acid group, an amine group, a thiol group, anepoxide group, an aziridine group, an azide group, a halide group, analkyne group, an olefin group, an acrylate group, a methacrylate group,and combinations thereof.
 5. Surface-modified nanoparticles according toclaim 3, wherein the non-polar compatibilizing group, if present, isselected from an alkyl group, an alkylene group, a heteroalkyl group, anaryl group, an arylene group, and combinations thereof. 6.Surface-modified nanoparticles according to claim 1, wherein the atleast one non-metallic organic derivative has the formula:

wherein R₁, is selected from the group consisting of hydrogen, an alkylgroup, a cycloalkyl group, an aryl group, a heteroaryl group, analkylaryl group, an alkylheteroaryl group and a heterocycloalkyl group,and wherein R₂ and R₃, independently, include a moiety selected from thegroup consisting of alkyl, alkylene, heteroalkyl, aryl, arylene, andcombinations thereof.
 7. Surface-modified nanoparticles according toclaim 6, wherein the organic derivative has a moiety included in R₂, R₃or both, that further comprises at least one group selected from thegroups consisting of hydroxyl groups, amino groups, thioether groups,thiol groups, carboxyl groups, carbonyl groups, ester groups, alkylethergroups, alkynyl groups, alkenyl groups, halogen groups, and combinationsthereof.
 8. Surface-modified nanoparticles according to claim 7, whereinone or more of the moieties comprises an acrylate or methacrylate ester.9. A sol comprising surface-modified nanoparticles according to claim 1.10. A method of making surface-modified nanoparticles comprising:combining an aqueous sol of acetate-functionalized zirconiananoparticles with at least one non-metallic organic derivativecomprising at least one N-hydroxyurea functionality, or a solutionthereof, to form a mixture; and removing water and displaced acetic acidfrom the mixture to form surface-modified nanoparticles.
 11. A methodaccording to claim 10, wherein the at least one non-metallic organicderivative further comprises a compatibilizing group.
 12. A methodaccording to claim 10, wherein the at least one compatibilizing group isselected from a hydroxyl group, a carboxylic acid group, an amine group,a thiol group, an epoxide group, an aziridine group, an azide group, ahalide group, an alkyne group, an olefin group, an acrylate group, amethacrylate group, and combinations thereof.
 13. A method according toclaim 11, wherein the at least one compatibilizing group is selectedfrom alkyl, alkylene, heteroalkyl, aryl, arylene, and combinationsthereof.
 14. A method according to claim 10, wherein the at least onenon-metallic organic derivative has the formula:

wherein R₁, is selected from the group consisting of hydrogen, an alkylgroup, a cycloalkyl group, an aryl group, a heteroaryl group, analkylaryl group, an alkylheteroaryl group and a heterocycloalkyl group,and wherein R₂ and R₃, independently, include a moiety selected from thegroup consisting of alkyl, alkylene, heteroalkyl, aryl, arylene, andcombinations thereof.
 15. A method according to claim 14, wherein thenon-metallic organic derivative has a moiety included in R₂, R₃ or both,that further comprises at least one group selected from the groupconsisting of hydroxyl groups, amino groups, thioether groups, thiolgroups, carboxyl groups, carbonyl groups, ester groups, alkylethergroups, alkynyl groups, alkenyl groups, halogen groups, (meth)acrylategroups, and combinations thereof.
 16. A composition comprising: anorganic matrix; and surface-modified zirconia nanoparticles attached toat least a portion of the organic matrix, wherein the surface-modifiednanoparticles comprise at least one non-metallic organic derivativecomprising at least one N-hydroxyurea functionality.
 17. A compositionaccording to claim 16, wherein the organic matrix is derived frommonomers, oligomers, copolymers, or a combination thereof.
 18. Acomposition according to claim 16 that is translucent or transparent.19. A composition according to claim 16 that is radioopaque.
 20. Acomposition according to claim 16 that has an index of refractiongreater than about 1.6.
 21. A composition according to claim 16 whereinthe organic matrix comprises a pressure-sensitive adhesive.